JP4342295B2 - Method for detecting inundation of optical cable and method for preparing maintenance plan of optical cable - Google Patents

Description

  The present invention relates to a method for performing maintenance by detecting inundation of an optical cable.

An optical fiber built-in overhead ground wire (hereinafter referred to as OPGW) is used as an important line for customers by renting an important line or a core wire in a power security communication line.
In recent years, there have been many examples in which the groove of an optical fiber built-in aluminum tube inside the OPGW is submerged due to aging or the like. This flooding causes freezing inside the OPGW in the winter, and communication failure due to optical fiber core wire microbending (minute distortion) occurs.
Conventionally, the failure detection of an optical fiber has been performed using a reflection type failure point rating device (hereinafter referred to as OTDR) for diagnosing the optical fiber.

On the other hand, a method has been proposed in which a light pulse is incident on an optical fiber and the presence or absence and / or location of the cable is detected based on the intensity ratio between the stroke side and the non-stroke side of the resulting Raman scattered light ing. (For example, see Patent Document 1.)
Further, it has been reported that an optical fiber filled with seawater shows an increase in loss in a specific wavelength band. (For example, see Non-Patent Document 1.)
JP 2003-222565 A NIKKEI ELECTRONICS 1984, 12.3 P.233 ~ P.248

By the way, even if a flooded cable is detected using the above-described conventional technology, a communication failure does not always occur, and how to predict the occurrence of a communication failure becomes a problem.
In addition, there is a problem of how to detect a flooded cable easily and accurately with respect to an optical cable in operation.

  The present invention has been made in view of such circumstances, and can easily detect a flooded cable with a simple method, and further predict the occurrence of a communication failure and create a maintenance plan from those that are likely to cause the failure. An object of the present invention is to provide an optical cable intrusion detection method and an optical cable maintenance plan creation method.

  In order to achieve the above object, an optical cable intrusion detection method according to the present invention selects at least two optical fibers of an optical cable in which optical fibers are housed, makes light of a specific wavelength enter each optical fiber, A difference in transmission loss between optical fibers is calculated, and the presence or absence of water in the optical cable is determined based on the difference in transmission loss.

As a result, it is possible to detect the inundation of the existing optical cable without attaching a new infiltration detection device or element to the optical cable.
Here, the “optical cable” is not limited to the structure, type, application, and the like of the cable, and includes, for example, various cables such as a power cable in which an optical fiber is accommodated and an overhead ground wire.
In particular, the optical cable is a plurality of overhead ground wires, and an optical fiber is selected from each of the different overhead ground wires.

  Preferably, in the above-described method for detecting inundation of an optical cable, after it is determined that there is inundation in the optical cable, a fault location is identified by a reflective failure point evaluation device (OTDR) or an optical fiber strain measurement device (BOTDR). Then, it becomes possible to identify both the location of failure and the cause of failure at the same time.

  The method for preparing an optical cable maintenance plan according to the present invention selects at least two optical fibers of an optical cable in which optical fibers are housed, makes light of a specific wavelength incident on each optical fiber, and connects between the optical fibers. A difference in transmission loss is calculated, a change with time in the difference in transmission loss is stored, and a maintenance plan is created based on the change with time.

Preferably, in the above-described optical cable maintenance plan creation method, the maintenance order is determined based on the magnitude of the transmission loss difference, and the maintenance plan is created based on the temperature and the temperature difference between day and night. Good.
This makes it possible to create a maintenance plan in descending order of the possibility of occurrence of communication failure due to freezing.

  According to the present invention, it is possible to detect a flooded cable with high accuracy by a simple method, and further, it is possible to predict the occurrence of a communication failure and create a maintenance plan from those that have a high possibility of occurrence of the failure.

Embodiments of the present invention will be described below. First, the principle of the cable flood detection method according to the present embodiment will be described.
The present embodiment utilizes the attenuation characteristics of light in a specific wavelength band described in Non-Patent Document 1. That is, the water that has entered the OPGW undergoes an electrochemical reaction with the aluminum tube containing the optical fiber to generate H2 (hydrogen) or OH group (hydroxyl group) ions. These ions pass through the optical fiber coating and chemically bond with Si (silicon) and Ge (germanium), which are the main constituents of the optical fiber, to generate SiOH and GeOH, and the H ₂ molecule has a dipole moment. Although they occur, they are known to absorb light in certain wavelength bands.

In the present embodiment, the transmission loss of a wavelength in a specific wavelength band is measured with the following configuration.
FIG. 1 is a configuration diagram of an apparatus for measuring the transmission loss of a specific wavelength and detecting the presence or absence of water immersion in an optical fiber. Here, the interface unit 6 of the measurement computer 1 is connected to the specific wavelength light source 2 and is connected to the channel selector A (3) via the connection fiber 7. The channel selector A (3) is further connected to the cable to be measured X (9) and the cable to be measured Y (10). The channel selector A (3) selects which of the cables to be measured X and Y to pass the light from the connection fiber 7 in accordance with a command from the measurement computer 1. Further, one ends of the cables to be measured X and Y are connected to the channel selector B (4) and connected to the power meter 5 through the connection fiber 8. The cables to be measured X and Y are preferably optical fibers that can be used as a backup line or a diagnostic line in the overhead ground wire. However, measurement is performed by optically multiplexing communication light and test light. Also good.

  The specific wavelength light source 2, the selectors A and B, and the power meter 5 are connected to the interface unit 6 of the measurement computer 1 and exchange data. Note that the measurement computer 1 is realized by a personal computer, and the interface unit 6 performs communication according to a standard such as GPIB. Further, it is assumed that a signal is transmitted between the interface unit 6 and each device via a relay transmission device (not shown) as necessary.

FIG. 2 is a functional block diagram of the measurement computer 1. Here, the measurement computer 1 processes an input unit 12 for inputting data and commands, a display unit 13 for displaying calculation results, an interface unit 6 for connecting to an external device such as a specific wavelength light source 2, and data processing. A central processing unit 11 for storing data, and a storage unit 14 for storing data. Further, the central processing unit 11 selects input / output processing means (function) 15 for transferring data to and from the input unit 12 or output unit 13 and a cable to be measured, and transmits a selection command to the selectors A and B. Measurement cable selection means 16, optical output command means (function) 17 for transmitting an output command to the specific wavelength light source 2, measurement result collection means (function) 18 for receiving data sent from the power meter 5, and measurement results The determination means 19 which determines the presence or absence of water immersion is provided.
In addition, the storage unit 14 includes a measurement file 20 that stores measurement results and determination results for each optical fiber.

  A method of detecting water immersion in the optical fiber using the apparatus configured as described above will be described with reference to FIG. First, as shown in FIG. 3, arbitrary two optical fibers are selected from the optical fibers at the same laying position to form a cable to be measured. Then, a command for selecting one of the two is sent from the input unit 12 (S101). This command is sent to the selectors A and B via the interface 6 by the measurement cable selection means 16. The selectors A and B perform switching so as to connect to the selected optical fiber for connection to the measured cable side.

  Then, a command for outputting light of a specific wavelength is input from the input unit 12 (S102). This command is sent to the specific wavelength light source 2 through the interface unit 6 by the optical output command means 17. The specific wavelength is effectively 1.24 μm or its vicinity. In addition to this wavelength band, a wavelength of 1.39 μm is also effective, but 1.24 μm is more effective because the attenuation tendency at the time of flooding becomes more prominent.

  The light emitted from the specific wavelength light source 2 enters the cable selected by the selector A through the connection optical fiber 7 and enters the power meter 5 from the selector B at the other end through the connection optical fiber 8. The light intensity is measured by the power meter 5, and the measurement result is input via the interface unit 6 of the measurement computer 1 and stored in the measurement file 20 by the measurement result collecting means 18 (S103).

Next, the measurement cable selection unit 16 transmits a selection command for switching to the other cable to be measured, and measures the light intensity of the cable to be measured as described above (S104 to S106).
When a series of measurements is completed, the determination means 19 is activated to determine whether there is water immersion. Specifically, when the determination unit 19 is activated, it calculates the transmission loss by obtaining the difference between the light output value of the specific wavelength light source and the measured value of the power meter 5 at the receiving end. Then, the difference in transmission loss between the two optical fibers is obtained (S107), and it is determined whether or not the difference is equal to or greater than a predetermined reference value (S108). (S109).

  FIG. 5 shows an example of a file storing reference values. If the difference in transmission loss between the two fibers is 5.0 dB / km or more, it is considered that there is a possibility of water immersion. This value may be changed in consideration of actual freezing and the possibility of the occurrence of microcracks based thereon. FIG. 6 is an example of a measurement file 20 that stores the results measured and calculated by the above processing. The distance between the two fibers, the injected light intensity, the received light intensity, the transmission loss obtained by subtracting the received light intensity from the injected light intensity, the loss difference that is the difference between the transmission losses of both optical fibers X and Y, and the reference value The comparison result is stored.

  According to the present embodiment, it is possible to detect the inundation of the existing optical fiber, so that it is possible to prevent a communication failure caused by microbending due to freezing by removing water from the cable or injecting antifreeze liquid into the cable. .

  As a method for detecting inundation, the wavelength of the light source to be generated is made variable, the loss is obtained for a series of wavelength bands, and the loss of a specific wavelength (eg, 1.24 μm) is a predetermined value relative to the loss of other wavelengths. Although it is possible to determine the presence or absence of water immersion depending on whether or not it is above, a light source having a variable wavelength is very expensive, and measuring a plurality of wavelengths takes time and labor. According to the present embodiment, since any two are selected and determined in the comparison, the apparatus can be configured at low cost and can be measured easily.

In particular, in the case of an overhead ground wire, as shown in FIG. 3, the cable is bent around the center of the tower as the lowest point. The number will increase. For this reason, it is effective to determine the presence or absence of water immersion in any two comparisons, and early detection of water immersion is also possible.
In addition, by using it also as OTDR, when a communication failure occurs, it is also possible to specify both the failure location and the cause of occurrence at the same time.

  Next, a second embodiment of the present invention will be described. FIG. 7 is a functional block diagram of the measurement computer 1 according to this embodiment. The main difference from FIG. 2 is that a maintenance plan creation means is provided and a maintenance plan table is added. In the present embodiment, light sources having wavelengths of 1.55 μm and 1.24 μm are used as the specific wavelength light sources.

  First, the intensity of the received light at the power meter is measured for each of the cables to be measured X and Y with a light source of 1.55 μm, and the difference between the two intensities is calculated and used as a correction value. Next, using the light source of 1.24 μm, the intensity of the received light is similarly measured for each of the cables to be measured X and Y, the difference between the two intensities is obtained, the correction value is subtracted from this value, and the corrected Find the value. If the corrected value is equal to or greater than a predetermined reference value, it is determined that there is water immersion.

FIG. 8 is an example of a measurement file in the present embodiment. A light source with a wavelength of 1.55 μm, which is a wavelength that is hardly affected by H ₂ molecules and OH groups, is used for correction.
FIG. 9 is an example of a maintenance plan table. If the loss difference is greater than or equal to a predetermined value (eg, “7.0”), the priority of maintenance is determined based on the minimum temperature, and if the minimum temperature is the same, the priority with the larger daytime / night temperature difference is increased. .
On the other hand, when the loss difference is less than or equal to a predetermined value, the order of maintenance is determined giving priority to the loss difference. This is performed for an optical fiber having a reference value (for example, “5.0”) or more that is a criterion for determining the possibility of flooding.

  Instead of prioritization by the above-described method, a weighting coefficient may be multiplied by the loss difference and the temperature, respectively, and priorities may be given as function values. Further, the difference in transmission loss may be observed periodically, the change with time may be stored, and the maintenance priority may be determined according to the degree of progress of loss.

  Note that it is also possible to determine whether or not an optical cable that has suffered a communication failure in the past is to be measured due to inundation. This determination is executed as a function of the measurement cable selection means. Hereinafter, a method for determining a measurement target regarding an optical cable in which a communication failure has occurred in the past will be described with reference to FIG.

First, a communication failure record is extracted (S201), and it is determined whether or not a communication failure has occurred (S202). Then, if a communication failure has occurred, the next occurrence time and occurrence time of the communication failure are extracted. Then, it is determined whether or not they are the time or time of the temperature drop (S204).
As a result, the maintenance plan is created with the highest priority of maintenance for the optical cable that is to be measured and whose loss difference is equal to or greater than a predetermined value as a result of the measurement.

  In the present embodiment, the difference in normal transmission loss for each optical cable is calculated and corrected using the calculated value. Therefore, in comparison with the first embodiment, the detection of inundation into the optical cable can be detected with higher accuracy. It becomes possible. In addition, since maintenance priorities are assigned using an increasing tendency of transmission loss with respect to a specific wavelength, temperature, and temperature difference, an efficient maintenance plan can be created.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention. For example, the specific wavelength for inundation detection is not limited to 1.24 μm or 1.39 μm, and any wavelength having a different light absorption rate depending on water can be used. Further, as a maintenance plan, in addition to the above, it is also possible to measure the absorptance of a plurality of specific wavelengths for a plurality of optical fibers and set the priority of maintenance depending on the difference in the absorptance.

It is a block diagram of the apparatus used for the water immersion detection method of the optical cable by the 1st Embodiment of this invention. FIG. 2 is a functional block diagram of the measurement computer 1 in FIG. 1. It is explanatory drawing of selection of the optical cable for a measurement by the 1st Embodiment of this invention. It is a flowchart which shows the procedure which detects the water immersion of an optical fiber. It is explanatory drawing of the file which memorize | stored the reference value. It is a data block diagram of the measurement file of FIG. It is a functional block diagram of the computer 1 for a measurement by the 2nd Embodiment of this invention. It is a data block diagram of the measurement file of FIG. It is a data block diagram of the maintenance plan table of FIG. It is a flowchart which shows the determination procedure of the measuring object regarding the optical cable in which communication failure has occurred in the past.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement computer 2 Specific wavelength light source 3, 4 Channel selector 5 Power meter 6 Interface part 7, 8 Connection optical fiber 9, 10 Cable to be measured 11 Central processing part 12 Input part 13 Display part 14 Storage part 15 Input / output processing Means 16 Measurement cable selection means 17 Optical output command means 18 Measurement result collection means 19 Determination means 20 Measurement file 21 Maintenance plan table 22 Maintenance plan creation means

Claims (6)

In a method for detecting water ingress in an optical cable containing an optical fiber,
The optical cable is an aerial ground wire. At least two optical fibers are selected from the aerial ground wire , light of a specific wavelength is incident on each optical fiber, and a difference in transmission loss between the optical fibers is calculated. An inundation detection method for an optical cable, wherein the presence or absence of inundation in the overhead ground wire is determined based on the difference in transmission loss. The method of claim 1, wherein the aerial ground wire is a plurality of aerial ground wires, and an optical fiber is selected from each of the different aerial ground wires.   3. The method for detecting inundation of an optical cable according to claim 1 or 2, wherein it is determined that there is inundation in the overhead ground wire, and then a fault location is identified by a reflective failure point evaluation device (OTDR) or an optical fiber strain measurement device (BOTDR). A method for detecting inundation of an optical cable, characterized in that: In a method for creating a maintenance plan for an optical cable containing optical fibers,
The optical cable is an aerial ground wire. At least two optical fibers are selected from the aerial ground wire , light of a specific wavelength is incident on each optical fiber, and a difference in transmission loss between the optical fibers is calculated. Determining the presence or absence of inundation in the overhead ground wire based on the difference in transmission loss, storing the change over time in the difference in transmission loss, and creating a maintenance plan based on the change over time, To create a maintenance plan for optical cables.   5. The method for preparing an optical cable maintenance plan according to claim 4, further comprising determining a maintenance order based on a difference in transmission loss.   6. The optical cable maintenance plan creation method according to claim 4, further comprising: creating a maintenance plan based on the temperature and the temperature difference between day and night.

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